This application claims the priority of 2458/96, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a gripping device for wafers which are stacked and spaced in a container as well as to a process for gripping and transporting the wafers.
The processing or handling of wafers such as semiconductor plates requires different process steps. Conventionally crude or unprocessed wafers are produced and are intermediately stored in containers. For the actual processing operation, these wafers must be removed from the container, must be supplied to an arrangement for carrying out the processing operation and must then be deposited again in a container. A basic problem during the overall processing and intermediate storage is the fact that the unprocessed wafers must be kept away from contaminations and dirt. Even the smallest contamination by dust or other particles causes damage to the corresponding area of the wafer surface. This damage can result in considerable failure rates of the end products produced from these wafers. For this reason, the processing normally takes place by so-called clean-room technology. That is, the processing zones must have a certain, determined cleanliness with respect to these dirt particles. The same also applies to the intermediate storage, i.e., the storage containers.
The removal and feeding of the wafers conventionally takes place either manually or automatically. The manual operation always increases the danger of a contamination. Hence an automatic operation is usually desired.
Conventionally, such wafers were produced and processed with a diameter of up to 200 mm. These wafers are conventionally stored in a vertically standing manner in cassettes which are especially designed for that purpose. For the removal and feeding, these wafers must only be taken in this vertical position out of the box and must be slid back into the box. For this purpose, suitable arrangements are known which come to a stop against the edge of the wafer. For this purpose, the wafers are inserted into rake-type holding devices which can simply be moved out of and into the boxes. The holding arrangements are designed such that the edge zones of the wafers are partially exposed so that the removal devices can be applied to this edge zone. The wafers can be touched by this device only on their edge sections extending perpendicularly to the surface as well as in a narrowly limited area on the periphery of the rear side.
Particularly newer larger wafers (up to 300 mm or larger) are now, for the most part, no longer stored vertically but horizontally in containers. These wafers must now be taken out of these containers and must then be swivelled into a different position, frequently by 90.degree., before they can be supplied to the downstream processing device. Conventionally no devices are known for this removal and swivel movement.
An object of the present invention is to provide a gripping device which can take horizontally stored wafers from their container and can feed them to a processing carrier in a swivelled position.
According to the present invention, this object has been achieved by a gripper device having at least one displaceable holding rake with slots configured to receive the wafers, swivellable rods provided with gripping heads having stop surfaces for stopping against edges of the wafers, and at least one counterholder having an elastic stop surface aligned substantially perpendicularly to a surface of the wafers.
The gripping device according to the present invention allows horizontally disposed wafers to be taken out of their storage container, swivelled, supplied to a processing carrier and positioned thereon. This completely meets the requirements concerning the area of the wafer which is not be touched by any objects because the gripping devices come in contact with the wafer essentially only at the edge and not on the disk surface. Nevertheless, the wafers are held in a stable manner and can therefore be swivelled advantageously into virtually any position. Advantageously, this can take place in a completely automated manner. The device can therefore be installed and operated in a closed-off area of a processing machine.
As the result of a preferred swivelling range of 90.degree., for the sliding-in between the stacked wafers, the gripping heads can advantageously be swivelled into their slide-in position. In this position, they can be moved without any problem into the space between the wafers without any contact with the surfaces of the wafers.
Because of the preferred feature of the holding or slot surfaces, the wafers are advantageously touched only on their marginal edge. That is, their surface is virtually untouched. This results particularly from the inclination of the slot surface directed against the bottom side of the wafers.
The same effect is achieved by a preferred aspect of the holding rake or the development of its slots. As a result, an advantageous secure and stable fit of the wafers is achieved without any change of their positions and particularly of their spacing.
Preferably, two gripping heads respectively are provided for one disk and come together, in a mutually spaced manner, to a stop against the edge area of one wafer respectively. For gripping of a stack of, for example, thirteen wafers, advantageously all gripping heads are simultaneously swivelled together.
Preferably, gripping devices of the aforementioned type according to the present invention are used in wafer processing systems. Furthermore, according to the present invention the process for achieving the object provides the step of while the container is open, displacing the gripping device, moving the grippers through an opening of the container between the wafers to edge areas thereof opposite the container opening, contacting the grippers with the edge areas of the wafers as a result of a pulling movement of the gripping device, and then displacing the counterholder from a starting position to come to a stop against an edge of the wafers, and lifting the wafers via the gripping device by lifting the wafers from a respective support in the container and removing the wafers from the container, and displacing the positioning rake, having one slot respectively for each of the wafers, against the edges of the wafers, whereupon the wafers come to rest against a stop in the slots, and then sliding the counterholder is back into the starting position.
Advantageously, before the wafer stack is removed from its container, the gripping device according to the present invention is slightly lifted so that the wafers are detached from their holding devices in the container. This approach prevents damage to the wafer surfaces by the holding devices which may occur if the wafers were simply pulled out and slide across the holding devices.